Impossible to migrate a month to month contract

For weeks now I have been trying to get my month-to-month contract that i switched to after the 2 year contract ended migrated to prepaid. Reference numbers ***3 (numerous emails and calls) on 23/12 and ***3 yesterday. Despite giving them plenty of notice to commence on 1/1 this was not done. I have email confirmation starting from 23/12 trying to retain me on contract which I did not want. on 1/1 they tried to debit the contract amount, I called and they said they would reverse it. I then get an sms demanding payment of the contract today. I have given up trying to get the call centre to fix it. I need the account to be transferred IMMEDIATELY onto prepaid. I will be porting this number, quite obviously, and need this sorted as it is sitting in limbo and I cannot make calls from it.